Such a power module generally includes a power module substrate having a ceramics substrate formed of AlN, Al2O3, Si3N4, or SiC and a conductive pattern, formed of pure aluminum or an aluminum alloy, provided on a surface of the ceramics substrate, a radiating element that is provided on the other surface of the ceramics substrate, a semiconductor chip, serving as a heating element, that is provided on an upper surface of the conductive pattern, and a cool sink that is provided on a lower surface of the radiating element. Heat from the heating element is dissipated to the outside through the radiating element and the cool sink.
Here, as disclosed in Japanese Patent No. 2953163, the conductive pattern is generally formed by joining a plate-shaped base material formed of pure aluminum or an aluminum alloy with the surface of the ceramics substrate by soldering or brazing, and then etching the base material. Such a conductive pattern formed by etching has a width to be gradually wider from the upper surface (heating element side) toward the lower surface (ceramics substrate side).
These days, a large-current, high-voltage, and compact power module, that is, a conductor having a narrower width constituting the conductive pattern and a narrower gap between the conductors is required.
First, in order to meet the former requirement, a conduction area of the conductive pattern needs to be increased. However, as for the large conduction area, since there is a limitation on design of the apparatus itself in which the power module is incorporated, the external size of the ceramics substrate cannot be increased, and thus the width and thickness of the conductor cannot be increased. In this case, as described above, if the conductive pattern is formed by etching, the width of a lower part of the conductor is increased by an increased width. For this reason, compactness as the latter requirement cannot be achieved. Accordingly, there is a problem in that both requirements are not satisfied simultaneously.
The increase in the thickness of the conductor results in an increase in the number of steps of etching, and manufacturing costs of the power module may be increased.
Meanwhile, in a technical field different from a technical field to which the invention belongs, an invention that can solve the above-described problems is disclosed in Japanese Unexamined Patent Application, First Publication No. H11-186679. That is, in a method of manufacturing an insulation substrate having a base insulating layer, an adhesion insulating layer, and a conductive pattern in that order, a conductive pattern member (conductor) obtained by performing press punching on a plate material is placed in an aligned state on the surface of the adhesion insulating layer in a B stage state, then the adhesion insulating layer and the adhesion insulating layer are joined with other by pressing, and subsequently a conductive pattern is provided on the surface of the adhesion insulating layer. In the insulation substrate formed in such a manner, the substantially entire side surface (a surface rising from the surface of the adhesion insulating layer) of the conductor constituting the conductive pattern is exposed.
However, when the conductive pattern is formed by etching the base material, ad described above, there is a problem in that much processing time is required and high-efficiency production is rarely realized. Further, the conductive pattern formed by etching is gradually wider from the upper surface side (heating element side) toward the lower surface side (ceramics substrate side). Accordingly, it is difficult to meet the recent requirements for a compact power module and reduction in the line width of the conductive pattern.
Further, like the invention described in Japanese Unexamined Patent Application, First Publication No. H11-186679, if the conductive pattern member (conductor) is formed by press punching, the rear side in a cutting direction of the cut surface, that is, a first cut surface (two-third of the thickness) has smaller surface roughness, but the front side in the cutting direction, that is, a second cut surface (one-third of the thickness) has larger surface roughness. If the insulation substrate is formed by applying the invention described in the Japanese Unexamined Patent Application, First Publication No. H11-186679, the power module is formed using the insulation substrate, and then the resultant power module is used, the power module may not be appropriately used. For example, the rise of the second cut surface may become a singular point and a spark may occur in that portion as a start point or the conductor may be electrically connected to an adjacent conductor.
The invention has been finalized in consideration of the above problems, and it is an object of the invention to provide a method of manufacturing a power module substrate that can realize high-efficiency production and reduction in the line width of a conductive pattern.
It is another object of the invention to provide an insulation substrate that can realize a large current and a high voltage of a power module, suppress an increase of the size of an insulation substrate in such a configuration, and realize low-cost production, a method of manufacturing an insulation substrate, a power module substrate, and a power module.